Electrospray ionisation and ion‐trap fragmentation of substituted 3,4‐dihydro‐2(1H)‐pyridin‐2‐ones

Abstract

A variety of 5-alkoxycarbonyl-4-aryl-6-methyl-3,4-dihydro-2(1H)-pyridones and hexahydrofuro[3,4-b]-2(1H)-pyridones have been investigated by electron impact (EI) and electrospray ionisation (ESI) techniques. Sequential product ion fragmentation (MS(n)) was performed to elucidate the degradation pathways for these compounds. Comparisons are made between positive and negative even-electron ions from ESI spectra and the molecular radical cations obtained under EI conditions. The data collected in this paper provide information on the strong impact that different substituents have on the ion fragmentation process.

Eco-Friendly Methodology to Prepare N-Heterocycles Related to Dihydropyridines: Microwave-Assisted Synthesis of Alkyl 4-Arylsubstituted-6-chloro-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylate and 4-Arylsubstituted-4,7-dihydrofuro[3,4-b]pyridine-2,5(1H,3H)-dione

“…The final products IIIa–i were characterized by melting point, NMR and mass spectral data. Most compounds synthesized in this study were known and their spectral characterization showed satisfactory agreement with the previous literature data [ 33 , 34 , 35 ]. The 1 H-NMR spectra of DHP derivatives IIIa–i showed one singlet corresponding to the NH at δ ~ 10.7–11.3 ppm.…”

“…In all cases, the MWAS yields for these compounds (Method A) were higher than those achieved previously with conventional synthesis conditions [ 33 , 34 , 35 ]. Moreover, the time of reaction was dramatically reduced from 12 h (720 min) in the conventional synthesis (Method B) to 10 min for the MWAS method.…”

“…Specifically, cyclohexanone and γ-lactone rings fused to the 1,4-DHP moiety result in a striking effect on the entry of calcium ions into the intracellular space (calcium antagonist effect) [ 32 ]. Our classical method for the synthesis of 4-arylsubstituted-4,7-dihydrofuro[3,4-b]pyridine-2,5(1H,3H)-diones III in moderate to good yields, comprised a one-pot reaction of the alkyl 2-methyl 6-oxo-1,4,5,6-tetrahydropyridine-3-carboxylates I with N -bromosuccinimide (NBS) as the brominating reagent by refluxing in chloroform in 12–14 h [ 33 , 34 , 35 ]. The microwave-accelerated lactonization to obtain the furo[3,4-b]pyridines IIIa–i were performed in a one-step procedure by reaction of previously synthesized I with NBS without solvent.…”

“…Table 2 shows the results obtained for the MWAS of compounds IIIa–i , compared with the classical method previously reported by our group (Method B) [ 33 , 34 , 35 ]. To check the possibility of intervention of specific non-pure thermal effects of MWs, the reaction was performed by heating in thermostated oil bath under the same experimental conditions used for MW irradiation (time, profiles of rise in temperature, vessels).…”

1H and 13C spectral assignment of 2(1H)‐pyridone derivatives

“…17 We have also reported the mass spectrometric behaviour of substituted 3,4-dihydro-2(1H)-pyridin-2-ones by electrospray ionization and ion-trap fragmentation methods. 18 This paper reports the complete 1 H and 13 C NMR assignments of a series of differently substituted 5-alkoxycarbonyl (1 and 2), 5-acetyl-4-aryl-3,4-dihydro-6-methyl-2(1H)pyridones (3) and pyridine derivatives 4 (Fig. 1).…”